The present invention relates to an electrical junction box for use in connection of wirings and circuits for electrical parts in an automobile.
In recent years, on-vehicle electrical parts and circuits have been increased more and more so as to meet the increasing needs of safety and comfortable driving of the automobile. On the other hand, a space for mounting the electrical parts such as an electrical junction box tends to be reduced because of the requirement of a sufficient compartment space.
FIG. 5 is a perspective view of a conventional electrical junction box as partly broken away, and FIG. 6 is a vertical sectional view of a part of the electrical junction box shown in FIG. 5. Referring to FIGS. 5 and 6, the electrical junction box includes an upper case 1 and a lower case 2 to be fitted with each other. In the upper case 1 and the lower case 2 is encased a stacked wiring board 5 formed by alternately stacking a plurality of bus bars 3 each having a desired pattern and a plurality of electrical insulating boards 4. A plurality of tab-like connection terminals 6 are formed by bending the bus bars 3 upwardly or downwardly. The connection terminals 6 project into connecting portions for various electrical parts such as connector receiving portions 7 and fuse receiving portions 8 provided on the upper case 1 or the lower case 2. An end connector 9 of a wire harness W is received into each connector receiving portion 7, and a fuse 10 is also received into each fuse receiving portion 8, so as to connect the end connector 9 and the fuse 10 with the connection terminals 6.
The bus bars 3 and the connection terminals 6 are formed by punching and bending a sheet metal in such a manner that different circuit patterns are formed according to destination, kind and grade of the automobile. That is, the bus bars 3 are manufactured to provide a dedicated circuit.
In the prior art electrical junction box including the above-mentioned bus bars formed by punching and bending and stacked to form the wiring board, it is hard to form the circuits with a high density for the following reasons. First, as each bus bar 3 is mechanically formed by punching a sheet metal, a minimum width of the bus bar 3 is limited such as normally at least about twice a thickness of the sheet metal. Accordingly, in the case that the bus bar 3 is applied to a signal circuit of one ampere or less, the minimum width becomes excessive. Secondly, as apparent from FIG. 6, since the electrical insulating board 4 is interposed between the bus bars 3 of different layers, heat conductivity in the electrical junction box is deteriorated. Therefore, an effect of radiation from the electrical junction box to the ambient air and the vehicle body is not so large. Thirdly, as the bus bars 3 are provided on the electrical insulating board 4, and these elements are stacked, it is necessary to ensure a spacing of at least 1.5-2 mm between the adjacent bus bars 3 on the same layer, and a plurality of ribs 4a for fixing the bus bars 3 are provided as required to avoid contact of the adjacent bus bars 3 on the same layer.
Furthermore, in changing the circuitry, it is necessary to change not only the corresponding bus bars but also the arrangement of the other bus bars on the same layer and the other layers as well as the connection terminals.
Additionally, the conventional bus bars having a stacked structure causes an increase in the number of parts, complication of the assembling operation, and an increase in manufacturing cost of a die.